ipv6 address design - texas ipv6 task force | ipv6 only, y'all!€¦ · · 2015-11-22......

IPv6 Address Design

A Few Practical Principles

Texas IPv6 Summit14 September, 2011

Copyright © 2011 Jeff Doyle and Associates, Inc.2

Foremost IPv4 address design consideration: Address Conservation

Balancing act between:– Number of subnets– Number of hosts on each subnet

Result: VLSM– Complex – Hard to manage

Legacy “class” categories still sometimes used in IPv4– Outdated and misleading

No such thing as subnet masks in IPv6– CIDR-style prefix length notation always used

Abandon IPv4 Thinking!

2001:db8:1234:abcd:5401:3c:15:85/48


IPv6 Global Unicast Address Structure

Subnet Interface ID

128 bits

Global Unicast Prefix

64 bits 64 bits

64 - n bitsn bits

Network (Location) Node (Identity)

Site TopologyPublic Topology

First 3 bits = 001


IPv4 developed 1973 – 1977

– 232 = 4.3 billion addresses

– More than anyone could possibly use!

IPv6 developed mid-1990s

– 2128 = 3.4 x 1038 addresses

– More than anyone could possibly use?

How Big is the IPv6 Address Space?

Galaxy UDFj-39546284


IPv4 developed 1973 – 1977

– 232 = 4.3 billion addresses

– More than anyone could possibly use!

IPv6 developed mid-1990s

– 2128 = 3.4 x 1038 addresses

– More than anyone could possibly use?

How Big is the IPv6 Address Space?

Galaxy UDFj-39546284

Some Perspective:

1 picometer = 10-12 (one trillionth) meter

232 picometers = 4.29 millimeters- length of a small ant

2128 picometers = 3.4 x 1023 kilometers- 34 billion light years- Furthest visible object in universe: 13.2B LYs


Typical IPv6 prefix assignments:– Service provider (LIR): /32 232 /64 subnets– Large end user: /48 65,536 /64 subnets – Small end user: /56 256 /64 subnets– SOHO: /64 or /60 1 or 16 /64 subnets

Address conservation is not a major consideration– Is this wasteful?– Yes! (But that’s okay)

If you don’t have enough subnets, you don’t have the right prefix allocation

In Practical Terms…


Simplicity– One-size-fits-all subnets

Manageability– Hex is much easier to interpret at binary level than

decimal

Scalability– Room to grow

Flexibility– Room to change

What Do I Get in Exchange for Waste?


Start by mapping “working” bits– Generally the bits between assigned prefix and Interface-ID

Group by hex digit– 4 bits per hex digit

Define “meanings” you need to operate– Geographic area? Logical topology? Type designation? User ID?

Try to keep “meanings” on hex boundaries– Defined meanings will then be some multiple of 24n

– Ex: 16, 256, 4096, 65,536…

Don’t get carried away with meanings– No need for 10 layers of address hierarchy if 4 will do

Designing for Simplicity


Use zero space as much as possible– Which address is easier to read?

• 2001:DB8:2405:83FC:72A6:3452:19ED:4727

• 2001:DB8:2405:C::27

Benefit: Operations quickly learns to focus on meaningful bits– Ignore public prefix (usually)

– Ignore Interface-ID (usually)

– A few hex digits tell operations most of what they need to know

Designing for Simplicity (continued)

2001:DB8:2405:C::27

Region Office Subnet


Leave “zero” space whenever possible

– Designate as Reserved

Insert between “meaningful” digits or bits

– Allows future expansion in two directions

Designing for Scale


Designing for Efficiency

By putting the bits most likely to be of interest to filters high in the bit order of the address, filter rules can be simplified


Trying to anticipate the unanticipated– A challenge for any kind of design

Another reason for well-placed Reserved (zero) space– Horizontal Reserved space

– Vertical Reserved space

Do not integrate IPv4 into an IPv6 design!– Reading IPv4 in hex is (almost) meaningless

– IPv4 will (eventually) go away

Designing for the Future


180 million trillion addresses in a /64 link

– And I will only ever use 2 of them?

– Are you kidding???

People have a very hard time accepting this

– Again: This is not IPv4!

– What else are you going to do with those addresses?

It’s a matter of comprehending the scale

– 500 out of 264 is not really any bigger than 2 out of 264

What About Point-to-Point Links?


Reasons for using /64– RFC 3627– RFC 5375 => /64 usage endorsed and encouraged– Design consistency– Anycast problems are not significant on PtP links

• Subnet-Router Ancast• MIPv6 Home Agent Anycast

Reasons for using /127– RFC 6164– Ping-pong vulnerability

• This is an issue with older version of ICMPv6 (RFC 2463)• Issue is corrected in newer version of ICMPv6 (RFC 4443)• Vendors: Upgrade your code!

– Neighbor cache exhaustion vulnerability

Don’t use /126– This is IPv4 thinking– “Subnet number” is meaningless in IPv6– IPv6 does not use broadcast addresses

Potential compromise:– Assign /64 per PtP subnet– Address /127 out of the /64

Point-to-Point Subnets


There is (currently) no NAT66 PI address assignment rules (varies by RIR):

– Must not be an LIR– Must be an end site – Must have previously justified a PI IPv4 assignment; or– Must currently be multihomed with IPv4; or

• And have an assigned ASN• Proposals to end this requirement

– Will make active use of 2000 IPv6 addresses within 12 months; or– Will make active use of 200 /64s within 12 months; or– Technical justification why cannot use assignment from LIR

PI assignment: One or more /48s– Larger based on number of sites

Micro-allocations available for critical Internet infrastructure

What About Provider Independence?


Some conflict of interpretation– Static route next hops

– BGP peering

IPv6 says use link local for direct connections

Accepted practice is to use global unicast

Recommendation: Stick with accepted practice– Link-local harder to manage

– Interface changes can change link-local address

Link Local vs Global Unicast


DNS design and management is critical

– DNS issues are well documented

IP Address Management is critical

– IPv6 design is not easy to manage via spreadsheets

– Good luck finding integrated DNS and DHCPv6 management

Abandon IPv4 thinking!

Other Issues


Questions?

[email protected]

www.doyleassociates.net

+1-303-428-4680

mailto:[email protected]

http://www.doyleassociates.net

ipv6 address design - texas ipv6 task force | ipv6 only, y'all!€¦ · · 2015-11-22......

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